1. Field of the Invention
The present invention relates to a flat panel display, and more particularly, to an active matrix organic light emitting diode (AMOLED) display and a manufacturing method thereof.
2. Description of the Prior Art
An organic light emitting diode display (OLED) is also called an organic light emitting diode. The OLED is one of the latest technologies rising in the middle of the twentieth century. Compared with a liquid-crystal display (LCD), the OLED has merits of all-solid-state, active illumination, high brightness, high contrast, thinness, lost costs, low power consumption, fast response, wide viewing angle, wide range of working temperature, easily flexible display, and so on. The OLED basically comprises a substrate, an anode, a cathode, and an organic functional layer. The light-emitting principle of the OLED is that positive and negative carriers are injected into an organic semiconductor thin-film and are conjugated through a plurality of very thin and laminated layers of organic material between the anode and the cathode for generating light. The organic functional layer of the OLED comprises three functional layers, that is, a hole transport layer (HTL), an emissive layer (EML), and an electron transport layer (ETL). Each of the functional layers can comprise one or more than one layer. For example, the HTL can sometimes be divided into a hole injection layer and a hole transport layer. The hole injection layer and the hole transport layer have similar functions, so they are generally called the HTL layer. The ETL can be divided into an electron transport layer and an electron injection layer. The electron transport layer and the electron injection layer have similar functions, so they are generally called the ETL layer.
Nowadays, the manufacturing method of a full-color OLED comprises three types: using three separate RGB OLEDs which emit red, blue, and green color, using a white OLED to emit white color incorporation with RGB color filters, and color conversion. The type of using three separate RGB OLEDs is the most potential of all because it is most frequently used in real applications. The manufacturing method of the type of using three separate RGB OLEDs is that using different lighting materials to manufacture the RGB OLEDs.
The OLED is divided into a passive driving and an active driving. In other words, the OLED is divided into direct addressing and addressing in a TFT matrix. The active driving OLED is an active matrix/organic light emitting diode (AMOLED), which is also called active matrix organic light emitting diode (AMOLED).
Please refer to FIG. 1. The conventional AMOLED comprises an OLED 100 and a TFT (thin-film transistor) 300 electrically connected to the OLED 100. The manufacturing method for the conventional AMOLED comprises following steps: forming the TFT 300 of which a pixel electrode serves as an anode 102 of the OLED 100, forming a hole transport layer (HTL) 104 on the anode 102, forming an emissive layer (EML) 106 on the HTL layer 104, forming an electron transport layer (ETL) 108 on the EML 106, and forming a cathode 110 on the ETL 108.
The conventional TFT 300 is produced after undergoing seven to ten photomask processes. The formation of the conventional TFT 300 is that a first insulation layer 302 is formed on the substrate 301; an active layer 303 is formed on the first insulation layer 302; a predetermined pattern is marked on the active layer 303 through a photomask process; a second insulation layer 304 is formed on the active layer 303; a first metallic layer is formed on the second insulation layer 304; a gate 305 is formed on the first metallic layer through a photomask process; a third insulation layer 306 is formed on the first metallic layer; a second metallic layer is formed on the third insulation layer 306; a source/drain 307 is formed on the second metallic layer through a photomask process; a fourth insulation layer 308 is formed on the second metallic layer; a pixel electrode (anode) 102 is formed on the fourth insulation layer 308; a fifth insulation layer 309 is formed on the pixel electrode 102; a predetermined pattern is marked on the fifth insulation layer 309 through a photomask process. Finally, the TFT 300 is produced.
With the increase in the resolution (high ppi), space for designing the pixel becomes inadequate. To compensate for the fault, a third metallic layer 310 (as shown in FIG. 2) is added on the fourth insulation layer 308 in the conventional TFT 300. A sixth insulation layer 311 is formed on the third metallic layer 310. One terminal of the third metallic layer 310 is electrically connected to the anode 102 of the OLED 100, and the other terminal of the third metallic layer 310 is electrically connected to the source/drain 307 of the conventional TFT 300 for facilitating conduction of the conventional TFT 300 and conduction of the OLED 100. In this way, more pixels can be designed.
However, two photomask processes have to be added in this method, which complicates the manufacturing process of the TFT and increases production costs greatly.